Photocatalytic paint, photocatalyst coating method, and photocatalyst-coated article

Abstract

To provide a photocatalytic paint which can form a photocatalyst layer having superior water resistance and durability while maintaining photocatalytic activity.SOLUTION: The photocatalytic paint of the present invention includes photocatalytic particles containing tungsten oxide, a binder, and an aqueous dispersion medium. The binder includes a first binder and a second binder, or a dehydrated condensate of the first binder and the second binder. The first binder is a compound containing a trihydroxysilane group or a dehydrated condensate of the compound, and the second binder is an aliphatic hydroxy acid or an aldonic acid.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a photocatalytic paint, a photocatalytic coating method, and a photocatalytic coated object. [Background technology]

[0002] Photocatalytic particles are particles that have photocatalytic activity generated by receiving light. By utilizing the photocatalytic activity, it is possible to, for example, decompose harmful substances in the air, decompose substances that cause bad odors, decompose pollutants dissolved or dispersed in water, decompose fungi, inhibit fungal growth, inhibit staining of exterior walls, or inhibit staining of windows. In order to utilize photocatalytic activity, it is necessary to fix photocatalytic particles to a substrate. For example, Patent Document 1 discloses an antifouling acrylic plate consisting of an acrylic substrate, a silica layer formed on the surface thereof, and a photocatalytic layer further formed on the silica layer. A bonding layer made of a silane coupling agent is provided between the surface of the acrylic substrate and the silica layer. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] WO2011 / 059101A1 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the acrylic plate disclosed in Patent Document 1, the substrate and the silica layer are merely bonded together by a silane coupling agent, which is insufficient in terms of improving the water resistance and durability of the photocatalyst layer. The present invention has been made in view of the above problems, and provides a photocatalytic coating material that can form a photocatalytic layer that is excellent in water resistance and durability while maintaining photocatalytic activity. [Means for solving the problem]

[0005] The present invention provides a photocatalytic coating material comprising photocatalytic particles containing tungsten oxide, a binder, and an aqueous dispersion medium, wherein the binder comprises a first binder and a second binder, or a dehydration condensate of the first binder and the second binder, wherein the first binder is a compound containing a trihydroxysilane group or a dehydration condensate of the compound, and the second binder is an aliphatic hydroxy acid or an aldonic acid. [Effects of the Invention]

[0006] By using the photocatalytic coating material of the present invention, it is possible to form a photocatalytic layer that is excellent in durability and water resistance while maintaining the stability over time and photocatalytic activity of the coating material. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is an explanatory diagram of a method for forming a photocatalytic layer using a photocatalytic coating material according to one embodiment of the present invention. [Figure 2] 1 is a conceptual diagram of a photocatalytic coating according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0008] The photocatalytic coating material of the present invention comprises photocatalytic particles containing tungsten oxide, a binder, and an aqueous dispersion medium, wherein the binder comprises a first binder and a second binder, or a dehydration condensate of the first binder and the second binder, the first binder being a compound containing a trihydroxysilane group or a dehydration condensate of the compound, and the second binder being an aliphatic hydroxy acid or an aldonic acid.

[0009] The compound containing the trihydroxysilane group is preferably a compound represented by chemical formula (1): R1-Si(OH)3 [wherein R1 represents an organic group having an epoxy group, an organic group having an amino group, an organic group having a methacryl group, or an organic group having a mercapto group], and the second binder is preferably a compound having one to five hydroxyl groups and one to three carboxyl groups. R1 in chemical formula (1) preferably represents a 3-glycidoxypropyl group, a 3-aminopropyl group, a 3-methacryloxypropyl group, or a 3-mercaptopropyl group.

[0010] The ratio (b / a) of the mass (b) of the binder to the total mass (a) of the photocatalytic particles and the binder in the photocatalytic coating material is preferably (1 / 100) or more and (25 / 100) or less. The ratio (c / a) of the mass (c) of the photocatalyst particles to the total mass (a) of the photocatalyst particles and the binder in the photocatalytic coating material is preferably (75 / 100) or more and (99 / 100) or less. The ratio (e / d) of the mass (e) of the second binder to the mass (d) of the first binder in the photocatalytic coating material is preferably (5 / 95) or more and (40 / 60) or less. The second binder is preferably gluconic acid, citric acid, malic acid or lactic acid. The photocatalytic coating material of the present invention preferably further contains a preservative, and the preservative preferably contains at least one of copper ions, silver ions, and zinc ions.

[0011] The present invention also provides a photocatalytic coating method comprising the steps of applying the photocatalytic coating material of the present invention onto a substrate to form a coating layer, and allowing the coating layer to dry naturally. The present invention also provides a photocatalytic coating that includes a substrate and a photocatalytic layer provided on the substrate, the photocatalytic layer including photocatalytic particles containing tungsten oxide and a dehydration condensate of a first binder and a second binder, wherein the first binder is a compound containing a trihydroxysilane group or a dehydration condensate of the compound, and the second binder is an aliphatic hydroxy acid or an aldonic acid.

[0012] The present invention will be described in more detail below with reference to several embodiments. The configurations shown in the drawings and the following description are examples, and the scope of the present invention is not limited to those shown in the drawings and the following description.

[0013] <First embodiment: photocatalytic paint> FIG. 1 is an explanatory diagram of a method for producing a photocatalyst-coated body using the photocatalyst coating material of this embodiment, and FIG. 2 is a conceptual diagram of a photocatalyst-coated object. The photocatalytic coating material 2 of this embodiment includes photocatalytic particles 12 containing tungsten oxide, a binder, and an aqueous dispersion medium. The binder includes a first binder and a second binder, or a dehydration condensate of the first binder and the second binder. The first binder is a compound containing a trihydroxysilane group or a dehydration condensate of the compound, and the second binder is an aliphatic hydroxy acid or an aldonic acid. The photocatalytic coating material 2 of this embodiment is applied to a substrate 3, and the coating layer 4 is dried to form a photocatalytic layer 5.

[0014] The photocatalytic paint 2 may be a suspension in which photocatalytic particles 12 are dispersed in an aqueous dispersion medium. The photocatalytic paint 2 may further contain an antiseptic containing at least one of copper ions, silver ions, and zinc ions, as necessary. The photocatalytic paint 2 is a water-based paint containing water. The solvent (or dispersion medium) of the photocatalytic paint 2 is water, a mixture of water and ethanol, or the like. This reduces the environmental load and improves the working environment.

[0015] The compound containing a trihydroxysilane group, which is the first binder, is, for example, a compound represented by chemical formula (1): R1-Si(OH)3. The first binder is, for example, a compound containing a trialkoxysilane group (R1-Si(OC n H 2n+1 The number of carbon atoms n is preferably 2 to 8. n H 2n+1 O-) is, for example, an ethoxy group (C2H5O-), which undergoes a hydrolysis reaction to become a hydroxyl group (-OH) (a silanol group SiOH) and ethanol. The first binder may also be a dehydration condensate of a compound represented by chemical formula (1). In the dehydration condensation reaction of the first binder, a hydroxyl group (silanol group) contained in one compound reacts with a hydroxyl group (silanol group) contained in another compound to generate water (HO), and two silicon atoms are bonded together by a siloxane bond. For example, a reaction such as the following formula occurs: 2R1-Si(OH)3 → R1-Si(OH)2OSi(OH)2-R1 + HO, generating the dehydration condensate, which is the first binder, and water. In the photocatalytic coating material 2, a part of the first binder may be chemically bonded to the second binder or the photocatalytic particles 12 by a dehydration condensation reaction.

[0016] R1 in chemical formula (1) represents, for example, an organic group having an epoxy group, an organic group having an amino group, an organic group having a methacryl group, or an organic group having a mercapto group. R1 in chemical formula (1) may also represent a 3-glycidoxypropyl group, a 3-aminopropyl group, a 3-methacryloxypropyl group, or a 3-mercaptopropyl group.

[0017] During the formation of the photocatalyst layer 5, the OH groups of the first binder undergo a dehydration condensation reaction with the OH groups of the second binder to form a siloxane compound (binder). The first binder also undergoes a dehydration condensation reaction with the hydroxyl (OH) groups on the surface of the photocatalyst particles 12, which are primarily composed of tungsten oxide. The first binder also undergoes a dehydration condensation reaction with the hydroxyl (OH) groups on the surface of the substrate 3 to bond. The first binder also easily bonds to the metal ions of the preservative. This allows the first binder to firmly bond to the preservative, the photocatalyst particles 12, the substrate 3 (e.g., metal, metal oxide, glass, and plastic), and the like. Therefore, the amount of binder required to form the photocatalyst layer 5 is smaller than the amount of the photocatalyst particles 12, preventing the photocatalytic function of the photocatalyst particles 12 from being impaired.

[0018] The second binder, an aliphatic hydroxy acid (hydroxycarboxylic acid, oxyacid, alcoholic acid), is a compound that has a carboxyl group (-COOH) and an alcoholic hydroxyl group (-OH) in one molecule, and does not have a six-membered ring consisting of six carbon atoms. The second binder, an aldonic acid, is a polyhydroxycarboxylic acid obtained by oxidizing the aldehyde group of an aldose. The second binder is, for example, a compound represented by the chemical formula (2): (HOOC) a R2(OH) b The second binder may be a compound having one to five hydroxyl groups (b=1 to 5) and one to three carboxyl groups (a=1 to 3). The second binder may be, for example, gluconic acid (HOOC-CH(OH)-CH(OH)-CH(OH)-CH(OH)-CH2OH), citric acid (HOOC-CH2-C(OH)(COOH)-CH2-COOH), malic acid (HOOC-CH(OH)-CH2COOH), or lactic acid (HC-CH(OH)COOH), with gluconic acid having many OH groups being particularly preferred. The second binder may be a non-volatile substance or a compound with low volatility. This stabilizes the pH of the photocatalytic coating material 2, allowing the photocatalytic coating material 2 to have stability over time. Since the second binder is an acidic substance, the photocatalytic coating material 2 becomes acidic. In the photocatalytic coating material 2, a part of the second binder may be chemically bonded to the first binder or the photocatalytic particles 12 by a dehydration condensation reaction.

[0019] The photocatalyst particles 12 are particles containing tungsten oxide as a main component, for example, tungsten oxide particles. The photocatalyst particles 12 may also be tungsten oxide particles having a co-catalyst on their surfaces. In the photocatalyst coating material 2, a portion of the photocatalyst particles 12 may be chemically bonded to the first binder or the second binder by a dehydration condensation reaction. The photocatalyst particles 12 have photocatalytic activity in the short wavelength region of visible light. Specifically, when the photocatalyst particles 12 are irradiated with light having an energy equal to or greater than the energy gap between the valence band and the conduction band, electrons in the valence band of the photocatalyst particles 12 are excited to the conduction band, generating holes in the valence band. These excited electrons reduce oxygen, generating superoxide anions. Furthermore, the generated holes oxidize water, generating hydroxyl radicals. The generated hydroxyl radicals generate reactive oxygen species. The generated reactive oxygen species are used to achieve, for example, the decomposition of harmful substances, antibacterial properties, and antifouling properties.

[0020] The tungsten oxide contained in the photocatalyst particles 12 is not particularly limited, and commercially available tungsten oxides can be used as appropriate. Examples of tungsten oxide include WO3 (tungsten trioxide), WO2, WO, W2O3, W4O5, and W4O. 11 , W 25 O 73 , W 20 O 58 , and W 24 O 68 and mixtures thereof. In order to improve the photocatalytic activity of the photocatalytic layer 5, WO3 is preferred as the tungsten oxide. A portion of the tungsten oxide may be reduced to a pentavalent tungsten oxide. However, it is preferred that the tungsten oxide be oxidized to a VI valent tungsten oxide before use. Examples of a method for oxidizing to a VI valent tungsten oxide include a method of calcining tungsten oxide at a high temperature. The crystal structure of the tungsten oxide is not particularly limited.

[0021] The average particle size of the photocatalyst particles 12, which are mainly composed of tungsten oxide, is preferably 5 nm or more and 200 nm or less. This makes the photocatalyst particles 12 less likely to aggregate and easier to redisperse. If the average particle size of the photocatalyst particles 12 is 200 nm or less, they tend to be more uniformly mixed with other paint components, and it is possible to prevent the photocatalyst particles 12 from detaching from the photocatalyst layer 5 formed by the photocatalyst paint 2. The average particle size is determined by the specific surface area (unit: m) of the particles measured by the BET method. 2 / g) and assuming that the primary particles are spherical.

[0022] The photocatalyst particles 12, which are primarily composed of tungsten oxide, preferably have promoter particles on their surfaces. The promoter particles are preferably metal particles, more preferably transition metal particles, and even more preferably platinum group metal particles. Examples of platinum group metal particles include Pt, Pd, Rh, Ru, Os, and IR particles. By providing promoter particles on the surfaces of the tungsten oxide particles, the energy gap between the valence band and conduction band of the tungsten oxide particles can be reduced, improving the photoresponse in the visible light region.

[0023] The photocatalytic coating 2 preferably contains a preservative in addition to the photocatalytic particles 12, which are primarily composed of tungsten oxide, a binder, and water. The preservative may contain copper ions, silver ions, or zinc ions. Water-soluble copper, silver, or zinc compounds may also be used as raw materials.

[0024] The ratio (b / a) of the mass (b) of the first and second binders to the total mass (a) of the photocatalyst particles 12 and the first and second binders in the photocatalytic coating material 2 is, for example, (1 / 100) or more and (25 / 100) or less. Also, the ratio (c / a) of the mass (c) of the photocatalyst particles 12 to the total mass (a) of the photocatalyst particles 12 and the first and second binders in the photocatalytic coating material 2 is, for example, (75 / 100) or more and (99 / 100) or less. This allows the photocatalyst layer 5 formed by applying and drying the photocatalyst coating material 2 to have durability and water resistance, and allows the photocatalyst layer 5 to have high photocatalytic activity.

[0025] When the coating layer 4 dries, the binder containing the first binder and the second binder or its dehydration condensate undergoes a dehydration condensation reaction with the photocatalyst particles 12 and also dehydration condenses with the substrate 3, thereby strongly bonding the photocatalyst particles 12 to the substrate 3 via the siloxane compound (binder). Therefore, even when the photocatalyst particle 12 content in the photocatalyst layer 5 is high, in other words, when the binder content is low, the photocatalyst particles 12 and the substrate 3 are strongly bonded via the binder (siloxane compound). This allows the amount of binder (containing the first binder and the second binder) added to the photocatalytic coating 2 to be reduced. This prevents the photocatalytic activity of the photocatalyst layer 5 from being impaired by the siloxane compound (binder) and also prevents the photocatalyst particles 12 from being buried in the siloxane compound (binder). As a result, the photocatalytic activity of the photocatalyst layer 5 can be particularly improved while improving its water resistance and durability.

[0026] The ratio (e / d) of the mass (e) of the second binder to the mass (d) of the first binder in the photocatalytic coating material 2 is, for example, not less than (5 / 95) and not more than (40 / 60). This makes the photocatalytic coating material 2 acidic, and when the coating layer 4 formed by applying the photocatalytic coating material 2 is dried, it is possible to proceed with dehydration condensation reactions between the first binders, between the first binder and the second binder, between the first binder and the photocatalytic particles 12, and between the first binder and the substrate 3. This allows the photocatalytic layer 5 formed by drying the coating layer 4 to have durability and water resistance.

[0027] <Second embodiment: Photocatalytic paint manufacturing method> The second embodiment of the present invention relates to a method for producing a photocatalytic coating material 2. The photocatalytic coating material 2 produced by the production method of the second embodiment is the photocatalytic coating material 2 of the first embodiment. For the same reasons as those described in the first embodiment, the photocatalytic layer 5 formed using the photocatalytic coating material 2 produced by the production method of the second embodiment is excellent in water resistance and durability while maintaining photocatalytic activity. The production method of the photocatalytic coating material 2 of the second embodiment includes, for example, a coating material preparation step.

[0028] (Paint preparation process) In the paint preparation step, the photocatalytic paint 2 of the first embodiment is obtained by mixing a first binder or its raw materials, a second binder, photocatalyst particles 12 mainly composed of tungsten oxide, and an aqueous dispersion medium. In order to improve dispersibility, it is preferable to mix the first and second binders with the photocatalyst particles 12 mainly composed of tungsten oxide. The photocatalyst particles 12 mainly composed of tungsten oxide may be added in the form of a photocatalytic liquid containing the photocatalyst particles 12 and a dispersion medium. The aqueous dispersion medium is, for example, water or a mixture of water and an alcohol (e.g., methanol, ethanol, propanol, etc.).

[0029] A compound containing a trialkoxysilane group, which is a raw material for the first binder, may be mixed with the second binder, and the solution containing the first and second binders after hydrolyzing the compound containing the trialkoxysilane group may be used to prepare the photocatalytic coating material 2. Because the second binder is an acidic substance, the mixed solution becomes acidic, and the hydrolysis reaction of the compound containing the trialkoxysilane group proceeds relatively quickly. Alternatively, a compound containing a trialkoxysilane group may be used in preparing the photocatalytic coating material 2, and the first binder may be produced by hydrolyzing the compound containing the trialkoxysilane group in the preparation of the photocatalytic coating material 2. Because the photocatalytic coating material 2 contains the second binder, which is an acidic substance, the hydrolysis reaction of the compound containing the trialkoxysilane group proceeds relatively quickly.

[0030] The compound containing trialkoxysilane group (R1-Si(OC)) is the raw material of the first binder. n H 2n+1) 3) is not water-soluble, while the hydrolyzate from which alcohol is eliminated by the hydrolysis reaction is water-soluble. Therefore, the completion of hydrolysis of the compound containing the trialkoxysilane group can be visually confirmed. Because the aqueous solution containing the second binder is acidic, it can promote the alcohol elimination reaction (hydrolysis reaction) of the raw material of the first binder. The OH groups of the second binder can bond by dehydration condensation with the silanol groups (hydroxyl groups) of the first binder after alcohol elimination. Furthermore, because the second binder is a non-volatile or low-volatile compound, the pH of the photocatalytic coating 2 is stable, maintaining the stability of the state of the first binder after hydrolysis and the dispersion stability of the photocatalytic particles 12. This allows the coating film quality and photocatalytic performance to be maintained over time.

[0031] <Third embodiment: photocatalytic coated material> The photocatalytic coated material 10 of this embodiment includes a substrate 3 and a photocatalytic layer 5 provided on the substrate 3. The photocatalytic layer 5 includes photocatalytic particles 12 containing tungsten oxide and dehydration condensation products 13 and 14 (siloxane compounds) of a first binder and a second binder, where the first binder is a compound containing a trihydroxysilane group or a dehydration condensation product of the compound, and the second binder is an aliphatic hydroxy acid or an aldonic acid. The photocatalytic layer 5 can have a configuration such as that shown in FIG. 2, for example.

[0032] Examples of materials for the substrate 3 (specifically, the support) include glass, plastic, metal, ceramics, wood, stone, cement, concrete, fiber, fabric, paper, leather, and combinations thereof. The substrate 3 may be a laminate having multiple layers of different materials. The material for the substrate 3 may be a material having hydroxy groups on its surface.

[0033] The photocatalytic layer 5 is provided on the substrate 3. The photocatalytic layer 5 may be disposed directly on the substrate 3. Alternatively, the photocatalytic layer 5 may be disposed on the substrate 3 via a primer layer. The primer layer is formed, for example, by a primer. The dehydration condensation products 13 and 14 (siloxane compounds) of the first binder and the second binder function as binders that bind the multiple photocatalyst particles 12 contained in the photocatalyst layer 5. The first binder can chemically bond to the photocatalyst particles 12 by undergoing a dehydration condensation reaction with the hydroxyl groups on the surfaces of the photocatalyst particles 12. Therefore, the dehydration condensation products 13 and 14 chemically bond to the multiple photocatalyst particles 12 contained in the photocatalyst layer 5, thereby enabling the multiple photocatalyst particles 12 to be strongly bonded together.

[0034] Furthermore, the dehydration condensation products 13 and 14 (siloxane compounds) of the first binder and the second binder also function as binders that bind the plurality of photocatalytic particles 12 contained in the photocatalyst layer 5 to the substrate 3. The first binder undergoes a dehydration condensation reaction with hydroxyl groups on the surface of the substrate 3 (or primer layer) to chemically bond to the substrate 3. Therefore, the dehydration condensation products 13 and 14 chemically bond to the plurality of photocatalyst particles 12 contained in the photocatalyst layer 5 and the substrate 3, thereby strongly bonding the plurality of photocatalyst particles 12 to the substrate 3. This allows the photocatalyst layer 5 to have excellent durability and excellent water resistance. Furthermore, the amounts of the dehydration condensation products 13 and 14 (siloxane compounds) contained in the photocatalyst layer 5 can be reduced, allowing the photocatalyst layer 5 to have excellent photocatalytic activity. As described above, the photocatalytic coating 10 has excellent water resistance and durability, and also has excellent photocatalytic activity, and therefore can exhibit photocatalytic activity suitably in any environment, such as indoors, outdoors, in the atmosphere, and underwater.

[0035] <Fourth embodiment: photocatalyst coating method> The photocatalytic coating method of this embodiment includes a coating step of coating the photocatalytic paint 2 of the first embodiment onto a substrate 3 to form a coating layer 4, and a drying step of drying the coating layer 4. A photocatalytic coated object 10 can be produced by this photocatalytic coating method. For example, a photocatalytic coated object 10 as shown in FIG. 1 can be produced. The photocatalytic coating method of this embodiment may also include a surface treatment step of performing a surface treatment on the substrate 3.

[0036] (Surface treatment process) Before applying the photocatalytic coating material 2 onto the substrate 3, the surface of the substrate 3 can be modified to be hydrophilic. By modifying the surface of the substrate 3 to be hydrophilic, the wettability of the photocatalytic coating material 2 to the substrate 3 can be improved, and a photocatalytic layer 5 having a more uniform film thickness can be formed. Examples of methods for modifying the surface of the substrate 3 to be hydrophilic include chemical treatment, mechanical treatment, corona treatment, flame treatment, ultraviolet irradiation treatment, high-frequency treatment, glow discharge treatment, plasma treatment, laser treatment, mixed acid treatment, and ozone oxidation treatment. Another example of a method for modifying the surface of the substrate 3 to be hydrophilic is a method of applying a primer to the substrate 3 to form a primer layer on the substrate 3. Among these methods, plasma treatment, ultraviolet irradiation treatment, corona treatment, or glow discharge treatment is preferred, and ultraviolet irradiation treatment is more preferred.

[0037] An example of ultraviolet irradiation treatment will be described. An ultraviolet irradiation device is used to irradiate the surface of the substrate 3 with ultraviolet rays. In this way, before the photocatalytic coating material 2 is applied onto the substrate 3, the surface of the substrate 3 is irradiated with ultraviolet rays to modify the surface of the substrate 3 to be hydrophilic. Since this facilitates modifying the surface of the substrate 3 to be hydrophilic, the wavelength of the ultraviolet rays is preferably 150 nm or more and 350 nm or less, and more preferably 200 nm or more and 300 nm or less. The device for irradiating ultraviolet rays is not particularly limited, and known devices can be used as appropriate. Examples of ultraviolet light sources include low-pressure mercury lamps and excimer lamps. The wavelength (λ) of the ultraviolet rays irradiated from the low-pressure mercury lamp is, for example, 254 nm and 185 nm. The wavelength (λ) of the ultraviolet rays irradiated from the excimer lamp is, for example, 308 nm (XeCl * lamp), 227 nm (KRCl * lamp), 172nm (Xe2 * lamp), 126nm (AR2 * lamp) and 146nm (KR2 * The duration of ultraviolet irradiation varies depending on the irradiance and irradiation conditions, but is, for example, from one minute to one hour.

[0038] (Coating process) In this step, a photocatalytic coating material 2 is applied onto a substrate 3 to form a coating layer 4 . The method for applying the photocatalytic coating material 2 onto the substrate 3 is not particularly limited. Examples of methods for applying the photocatalytic coating material 2 onto the substrate 3 include spin coating, dipping, spraying, roll coating, gravure coating, wire bar coating, air knife coating, and inkjet coating. The photocatalytic coating material 2 only needs to be applied to at least a portion of the substrate 3. The thickness of the photocatalytic layer 5 to be formed is not particularly limited. Regardless of the thickness of the photocatalytic layer 5 obtained by any application method, the photocatalytic layer 5 can have excellent durability.

[0039] (drying process) In this step, the coating layer 4 is dried. There are no particular limitations on the method for drying the photocatalytic coating 2 (coating layer 4) applied to the substrate 3. Examples of methods for drying the photocatalytic coating 2 (coating layer 4) applied to the substrate 3 include room temperature drying, air drying, forced drying using a dryer, and baking. The temperature for drying the photocatalytic coating 2 (coating layer 4) applied to the substrate 3 is preferably 20°C or higher and 150°C or lower.

[0040] In the drying process, the aqueous dispersion medium contained in the coating layer 4 gradually evaporates, reducing the water content. Therefore, the first binder and the second binder contained in the coating layer 4 are concentrated, and a dehydration condensation reaction between the hydroxyl groups (silanol groups) of one of the first binders and the hydroxyl groups (silanol groups) of the other first binder, a dehydration condensation reaction between the hydroxyl groups (silanol groups) of the first binder and the hydroxyl groups of the second binder, a dehydration condensation reaction between the hydroxyl groups (silanol groups) of the first binder and the hydroxyl groups of the photocatalyst particles 12, and a dehydration condensation reaction between the hydroxyl groups (silanol groups) of the first binder and the hydroxyl groups of the substrate 3 proceed, gradually forming dehydration condensates 13 and 14 (siloxane compounds). Therefore, by thoroughly drying the coating layer 4, a photocatalyst layer 5 having excellent durability and excellent water resistance can be formed.

[0041] <Preparation of photocatalytic paint> Photocatalytic coating materials 1 to 20 having the compositions shown in Table 1 (mass when the dehydration condensation reaction has not progressed) were prepared.

[0042] [Table 1]

[0043] "Pt-WO3" in Table 1 indicates platinum-supported tungsten oxide particles (photocatalyst particles). The preparation of a 20 wt% photocatalyst dispersion liquid containing platinum-supported tungsten oxide particles will be described later. "B-1" (first binder) in Table 1 represents 3-glycidoxypropyltrihydroxysilane. 3-Glycidoxypropyltrihydroxysilane is produced by hydrolysis of the raw material 3-glycidoxypropyltriethoxysilane during the preparation process of the photocatalytic paint. The photocatalytic paint is acidic because it contains Pt-WO3 or a second binder, which causes the hydrolysis reaction of 3-glycidoxypropyltriethoxysilane to proceed.

[0044] "B-2" (first binder) in Table 1 represents 3-aminopropyltrihydroxysilane. 3-Aminopropyltrihydroxysilane is produced by hydrolysis of the raw material 3-aminopropyltriethoxysilane during the preparation process of the photocatalytic paint. The photocatalytic paint is acidic because it contains Pt-WO3 or a second binder, which causes the hydrolysis reaction of 3-aminopropyltriethoxysilane to proceed. Photocatalytic paints 13 to 15, 18, and 20 contain both 3-glycidoxypropyltrihydroxysilane and 3-aminopropyltrihydroxysilane as the first binder, and the ratio (b / a) of the mass (b) of 3-aminopropyltrihydroxysilane to the mass (a) of 3-glycidoxypropyltrihydroxysilane is 1 / 1. In addition, the content of the first binder contained in photocatalytic paints 13 to 15, 18, and 20 in Table 1 is the total mass of 3-glycidoxypropyltrihydroxysilane and 3-aminopropyltrihydroxysilane.

[0045] "B-3" (second binder) in Table 1 represents gluconic acid (HOOC-CH(OH)-CH(OH)-CH(OH)-CH(OH)-CHOH). "B-4" (second binder) in Table 1 represents citric acid (HOOC-CH2-C(OH)(COOH)-CH2-COOH). When mixed with water, these become acidic, which promotes the hydrolysis reaction of the raw materials "B-1" and "B-2," 3-glycidoxypropyltriethoxysilane and 3-aminopropyltriethoxysilane, and reacts with the silanol after hydrolysis to become binder components. Pure water was used as "water" in Table 1. "-" in Table 1 indicates that the paint does not contain the corresponding material.

[0046] Table 1 shows the ratio of the mass of the first and second binders ((1) + (2)) to the total mass ((1) + (2) + (3)) of the first binder (1), the second binder (2), and the photocatalyst particles (3). Table 1 shows the ratio of the mass (2) of the second binder to the mass (1) of the first binder. Table 1 shows the ratio of the total mass ((1)+(2)+(3)) of the first and second binders and the photocatalytic particles to the mass of the photocatalytic coating material.

[0047] [Preparation of 20 wt% photocatalyst dispersion] Platinum-loaded tungsten oxide particles (Pt-WO3), which are photocatalytic particles, were prepared using the following method. Specifically, 200 g of tungsten oxide (Kishida Chemical Co., Ltd.) was mixed with 1000 mL of pure water and then dispersed under ultrasonic irradiation to obtain tungsten oxide particle dispersion A. Platinum(VI) hexachlorohexahydrate (Kishida Chemical Co., Ltd., purity 98.5%) was dissolved in dispersion A to obtain tungsten oxide particle dispersion B. The amount of hexachloroplatinum(VI) hexahydrate added was adjusted so that the ratio of the weight of platinum to the weight of the tungsten oxide particles was 0.05 wt%. Platinum-loaded tungsten oxide particles (Pt-WO3) were prepared by heating dispersion B at 100°C to evaporate the water and calcining it.

[0048] The prepared platinum-supported tungsten oxide particles were mixed with pure water so that the ratio of the platinum-supported tungsten oxide particles in the photocatalyst dispersion was 20 wt%. The resulting mixture was irradiated with ultrasound to disperse the platinum-supported tungsten oxide particles (average particle diameter: 175 nm) and prepare a 20 wt% photocatalyst dispersion.

[0049] [Preparation of photocatalytic paint 1] 3-glycidoxypropyltriethoxysilane, the raw material for 3-glycidoxypropyltrihydroxysilane, gluconic acid, pure water, and a 20 wt% photocatalyst dispersion were mixed to obtain Photocatalyst Paint 1 (100 g) with a total solids concentration of 6.3 mass % so that the composition of Photocatalyst Paint 1 would be as shown in Table 1. The total solids concentration is the ratio of the total mass of the first and second binders and the photocatalyst particles ((1) + (2) + (3)) to the mass of the photocatalyst paint. The same applies below. In photocatalytic coating 1, the mass ratio ((1)+(2)) / ((1)+(2)+(3)) is (20 / 100), and the mass ratio ((2) / (1)) is (5 / 95).

[0050] [Preparation of photocatalytic paint 2] 3-glycidoxypropyltriethoxysilane, which is the raw material for 3-glycidoxypropyltrihydroxysilane, gluconic acid, pure water, and a 20 wt% photocatalyst dispersion were mixed so that the composition of photocatalyst coating 2 would be as shown in Table 1, thereby obtaining photocatalyst coating 2 (100 g) with a total solids concentration of 6.3 mass%. In photocatalytic coating 2, the mass ratio ((1)+(2)) / ((1)+(2)+(3)) is (20 / 100), and the mass ratio ((2) / (1)) is (20 / 80).

[0051] [Preparation of photocatalytic paint 3] 3-glycidoxypropyltriethoxysilane, which is the raw material for 3-glycidoxypropyltrihydroxysilane, gluconic acid, pure water, and a 20 wt% photocatalyst dispersion were mixed so that the composition of photocatalyst coating 3 would be as shown in Table 1, thereby obtaining photocatalyst coating 3 (100 g) with a total solids concentration of 6.3 mass%. In photocatalytic coating 3, the mass ratio ((1)+(2)) / ((1)+(2)+(3)) is (20 / 100), and the mass ratio ((2) / (1)) is (40 / 60).

[0052] [Preparation of photocatalytic paint 4] 3-glycidoxypropyltriethoxysilane, which is the raw material for 3-glycidoxypropyltrihydroxysilane, gluconic acid, pure water, and a 20 wt% photocatalyst dispersion were mixed so that the composition of photocatalyst coating 4 would be as shown in Table 1, thereby obtaining photocatalyst coating 4 (100 g) with a total solids concentration of 5.6 mass%. In photocatalytic coating 4, the mass ratio ((1)+(2)) / ((1)+(2)+(3)) is (10 / 100), and the mass ratio ((2) / (1)) is (5 / 95).

[0053] [Preparation of photocatalytic paint 5] 3-glycidoxypropyltriethoxysilane, which is the raw material for 3-glycidoxypropyltrihydroxysilane, gluconic acid, pure water, and a 20 wt% photocatalyst dispersion were mixed so that the composition of photocatalyst paint 5 would be as shown in Table 1, thereby obtaining photocatalyst paint 5 (100 g) with a total solids concentration of 5.6 mass%. In the photocatalytic coating 5, the mass ratio ((1)+(2)) / ((1)+(2)+(3)) is (10 / 100), and the mass ratio ((2) / (1)) is (20 / 80).

[0054] [Preparation of photocatalytic paint 6] 3-glycidoxypropyltriethoxysilane, which is the raw material for 3-glycidoxypropyltrihydroxysilane, gluconic acid, pure water, and a 20 wt% photocatalyst dispersion were mixed so that the composition of photocatalyst coating 6 would be as shown in Table 1, thereby obtaining photocatalyst coating 6 (100 g) with a total solids concentration of 5.6 mass%. In the photocatalytic coating 6, the mass ratio ((1)+(2)) / ((1)+(2)+(3)) is (10 / 100), and the mass ratio ((2) / (1)) is (40 / 60).

[0055] [Preparation of photocatalytic paint 7] 3-glycidoxypropyltriethoxysilane, which is the raw material for 3-glycidoxypropyltrihydroxysilane, gluconic acid, pure water, and a 20 wt% photocatalyst dispersion were mixed so that the composition of photocatalyst paint 7 would be as shown in Table 1, thereby obtaining photocatalyst paint 7 (100 g) with a total solids concentration of 5.1 mass%. In the photocatalytic coating 7, the mass ratio ((1)+(2)) / ((1)+(2)+(3)) is (1 / 100), and the mass ratio ((2) / (1)) is (5 / 95).

[0056] [Preparation of photocatalytic paint 8] 3-glycidoxypropyltriethoxysilane, which is the raw material for 3-glycidoxypropyltrihydroxysilane, gluconic acid, pure water, and a 20 wt% photocatalyst dispersion were mixed so that the composition of photocatalyst coating 8 would be as shown in Table 1, thereby obtaining photocatalyst coating 8 (100 g) with a total solids concentration of 5.1 mass%. In the photocatalytic coating 8, the mass ratio ((1)+(2)) / ((1)+(2)+(3)) is (1 / 100), and the mass ratio ((2) / (1)) is (20 / 80).

[0057] [Preparation of photocatalytic paint 9] 3-glycidoxypropyltriethoxysilane, which is the raw material for 3-glycidoxypropyltrihydroxysilane, gluconic acid, pure water, and a 20 wt% photocatalyst dispersion were mixed so that the composition of photocatalyst coating 9 would be as shown in Table 1, thereby obtaining photocatalyst coating 9 (100 g) with a total solids concentration of 5.1 mass%. In the photocatalytic coating 9, the mass ratio ((1)+(2)) / ((1)+(2)+(3)) is (1 / 100), and the mass ratio ((2) / (1)) is (40 / 60).

[0058] [Preparation of photocatalytic paint 10] 3-glycidoxypropyltriethoxysilane, which is the raw material for 3-glycidoxypropyltrihydroxysilane, citric acid, pure water, and a 20 wt% photocatalyst dispersion were mixed so that the composition of photocatalyst coating 10 would be as shown in Table 1, thereby obtaining photocatalyst coating 10 (100 g) with a total solids concentration of 5.6 mass%. In the photocatalytic coating 10, the mass ratio ((1)+(2)) / ((1)+(2)+(3)) is (10 / 100), and the mass ratio ((2) / (1)) is (5 / 95).

[0059] [Preparation of photocatalytic paint 11] 3-glycidoxypropyltriethoxysilane, which is the raw material for 3-glycidoxypropyltrihydroxysilane, citric acid, pure water, and a 20 wt% photocatalyst dispersion were mixed so that the composition of photocatalyst coating 11 would be the composition shown in Table 1, thereby obtaining photocatalyst coating 11 (100 g) with a total solids concentration of 5.6 mass%. In the photocatalytic coating 11, the mass ratio ((1)+(2)) / ((1)+(2)+(3)) is (10 / 100), and the mass ratio ((2) / (1)) is (20 / 80).

[0060] [Preparation of photocatalytic paint 12] 3-glycidoxypropyltriethoxysilane, which is the raw material for 3-glycidoxypropyltrihydroxysilane, citric acid, pure water, and a 20 wt% photocatalyst dispersion were mixed so that the composition of photocatalyst coating 12 would be as shown in Table 1, thereby obtaining photocatalyst coating 12 (100 g) with a total solids concentration of 5.6 mass%. In the photocatalytic coating 12, the mass ratio ((1)+(2)) / ((1)+(2)+(3)) is (10 / 100), and the mass ratio ((2) / (1)) is (40 / 60).

[0061] [Preparation of photocatalytic paint 13] 3-glycidoxypropyltriethoxysilane, a raw material for 3-glycidoxypropyltrihydroxysilane, 3-aminopropyltriethoxysilane, a raw material for 3-aminopropyltrihydroxysilane, gluconic acid, pure water, and a 20 wt% photocatalyst dispersion were mixed so that the composition of photocatalyst coating 13 would be as shown in Table 1, thereby obtaining photocatalyst coating 13 (100 g) with a total solids concentration of 5.6 mass%. In the photocatalytic coating 13, the mass ratio ((1)+(2)) / ((1)+(2)+(3)) is (10 / 100), and the mass ratio ((2) / (1)) is (5 / 95).

[0062] [Preparation of photocatalytic paint 14] 3-glycidoxypropyltriethoxysilane, a raw material for 3-glycidoxypropyltrihydroxysilane, 3-aminopropyltriethoxysilane, a raw material for 3-aminopropyltrihydroxysilane, gluconic acid, pure water, and a 20 wt% photocatalyst dispersion were mixed so that the composition of photocatalyst coating 14 would be as shown in Table 1, thereby obtaining photocatalyst coating 14 (100 g) with a total solids concentration of 5.6 mass%. In the photocatalytic coating 14, the mass ratio ((1)+(2)) / ((1)+(2)+(3)) is (10 / 100), and the mass ratio ((2) / (1)) is (20 / 80).

[0063] [Preparation of photocatalytic paint 15] 3-glycidoxypropyltriethoxysilane, a raw material for 3-glycidoxypropyltrihydroxysilane, 3-aminopropyltriethoxysilane, a raw material for 3-aminopropyltrihydroxysilane, gluconic acid, pure water, and a 20 wt% photocatalyst dispersion were mixed so that the composition of photocatalyst coating 15 would be as shown in Table 1, thereby obtaining photocatalyst coating 15 (100 g) with a total solids concentration of 5.6 mass%. In the photocatalytic coating 15, the mass ratio ((1)+(2)) / ((1)+(2)+(3)) is (10 / 100), and the mass ratio ((2) / (1)) is (40 / 60).

[0064] [Preparation of photocatalytic paint 16] Pure water and a 20 wt % photocatalyst dispersion were mixed so that the composition of the photocatalyst coating 16 would be the composition shown in Table 1, to obtain a photocatalyst coating 16 (100 g) with a total solids concentration of 5.0 mass %. The photocatalytic coating 16 does not contain the first or second binder.

[0065] [Preparation of photocatalytic paint 17] 3-glycidoxypropyltriethoxysilane, which is the raw material for 3-glycidoxypropyltrihydroxysilane, was mixed with pure water and a 20 wt% photocatalyst dispersion so that the composition of photocatalyst coating 17 would be as shown in Table 1, thereby obtaining photocatalyst coating 17 (100 g) with a total solids concentration of 5.5 mass%. In the photocatalytic coating 17, the mass ratio ((1)+(2)) / ((1)+(2)+(3)) is (10 / 100). The photocatalytic coating 17 does not contain a second binder.

[0066] [Preparation of photocatalytic paint 18] 3-glycidoxypropyltriethoxysilane, a raw material for 3-glycidoxypropyltrihydroxysilane, 3-aminopropyltriethoxysilane, a raw material for 3-aminopropyltrihydroxysilane, pure water, and a 20 wt% photocatalyst dispersion were mixed together to obtain photocatalyst coating 18 (100 g) with a total solids concentration of 5.5 mass% so that the composition of photocatalyst coating 18 would be as shown in Table 1. In the photocatalytic coating 18, the mass ratio ((1)+(2)) / ((1)+(2)+(3)) is (10 / 100). The photocatalytic coating 18 does not contain a second binder.

[0067] [Preparation of photocatalytic paint 19] 3-glycidoxypropyltriethoxysilane, which is the raw material for 3-glycidoxypropyltrihydroxysilane, gluconic acid, pure water, and a 20 wt% photocatalyst dispersion were mixed so that the composition of photocatalyst paint 19 would be as shown in Table 1, thereby obtaining photocatalyst paint 19 (100 g) with a total solids concentration of 7.1 mass%. In the photocatalytic coating 19, the mass ratio ((1)+(2)) / ((1)+(2)+(3)) is (30 / 100), and the mass ratio ((2) / (1)) is (20 / 80).

[0068] [Preparation of photocatalytic paint 20] 3-glycidoxypropyltriethoxysilane, a raw material for 3-glycidoxypropyltrihydroxysilane, 3-aminopropyltriethoxysilane, a raw material for 3-aminopropyltrihydroxysilane, gluconic acid, pure water, and a 20 wt% photocatalyst dispersion were mixed so that the composition of photocatalyst coating 20 would be as shown in Table 1, thereby obtaining photocatalyst coating 20 (100 g) with a total solids concentration of 7.1 mass%. In the photocatalytic coating 20, the mass ratio ((1)+(2)) / ((1)+(2)+(3)) is (30 / 100), and the mass ratio ((2) / (1)) is (20 / 80).

[0069] <Photocatalytic paint evaluation method and evaluation results> [Preparation of photocatalyst for evaluation] Photocatalyst coatings 1 to 20 were used to prepare evaluation photocatalysts 1 to 20, each having a photocatalyst layer on a substrate. Evaluation photocatalyst 1 was prepared using photocatalyst coating 1, and evaluation photocatalysts 2 to 20 were also prepared using photocatalyst coatings with the same reference numerals. Furthermore, two of each of evaluation photocatalysts 1 to 20 were prepared (one for a durability test and one for a methylene blue decomposition test). The substrates used to prepare the evaluation photocatalysts 1 to 20 were as follows. Substrate: Non-alkali glass (length 50 mm, width 50 mm, thickness 0.5 mm)

[0070] First, the substrate was subjected to a treatment (UV ozone cleaning treatment) in which ultraviolet rays were irradiated onto the substrate for 30 minutes using an ultraviolet ozone irradiation device (manufactured by Technovision, model: UV-312) equipped with a low-pressure mercury lamp. In this way, the surface of the substrate was modified to be hydrophilic. Next, the thickness (basis weight) of the coating film (photocatalytic layer) after drying of the photocatalytic paint applied to the substrate was adjusted to 5.0 g / m. 2The photocatalytic coating was applied to the substrate multiple times using a trigger spray until the photocatalytic coating became uniform, and the applied layer was dried for one day at 25° C. In this way, photocatalysts 1 to 20 for evaluation, each having a photocatalyst layer on a substrate, were obtained.

[0071] [Durability test] A durability test was carried out by the following method. Four mending tapes (3M Model No. 810-3-12 tape cut to a length of 50 mm and a width of 12 mm) were attached in parallel to the surface of the photocatalytic layer of evaluation photocatalysts 1 to 20. Next, the four mending tapes were peeled off from the surface of the photocatalyst layer. The adhesive surfaces of the four peeled mending tapes were visually observed to confirm whether or not the peeled photocatalyst layer was still attached. The evaluation results of the durability of the evaluation photocatalysts 1 to 20 are shown in Table 2. The evaluation criteria for durability are as follows. ◯: No adhesion of the photocatalytic layer peeled off from the substrate was observed on any of the four mending tapes. △: Peeled photocatalytic layer was observed adhering to the substrate on one of the four mending tapes. ×: Photocatalytic layer peeled off from the substrate was observed adhering to two or more of the four mending tapes.

[0072] [Table 2]

[0073] The durability test evaluation of the evaluation photocatalysts 1 to 15, 19, and 20 formed using photocatalyst coatings 1 to 15 (Examples 1 to 15) and photocatalyst coatings 19 and 20 (Comparative Examples 4 and 5) was evaluated as "Good." These photocatalyst coatings contain both the first binder and the second binder, which is thought to be why the photocatalyst layer is strongly bonded to the substrate. The durability test of the evaluation photocatalyst 16 formed using the photocatalyst coating material 16 (Comparative Example 1) was evaluated as "X." Since the photocatalyst coating material 16 does not contain the first binder or the second binder, it is thought that the bonding of the photocatalyst layer to the substrate is weak. The durability test evaluation of the evaluation photocatalyst bodies 17 and 18 formed using the photocatalyst paints 17 and 18 (Comparative Examples 2 and 3) was evaluated as "△." Photocatalyst paints 17 and 18 contain the first binder but do not contain the second binder, which is thought to result in weaker bonding of the photocatalyst layer to the substrate than the evaluation photocatalyst bodies 1 to 15, 19, and 20.

[0074] [Methylene blue decomposition test] A methylene blue decomposition test (measurement of methylene blue fading rate), which is a test to confirm photocatalytic activity, was conducted using each of the evaluation photocatalysts 1 to 20 by the method described below. 20 μL of methylene blue reagent with a concentration of 100 μmol / L was dropped onto the photocatalytic layer of the evaluation photocatalyst using a micropipette. The methylene blue reagent dropped onto the evaluation photocatalyst was dried at room temperature. Next, an ultraviolet lamp was used to measure the fading rate of methylene blue, which is a test to confirm photocatalytic activity at a peak emission wavelength of 365 nm and an irradiance of 2.5 mW / cm. 2 The photocatalyst for evaluation was irradiated with ultraviolet light of 1000 kJ / s at 1000 kJ / s for 24 consecutive hours. The fading rate of methylene blue dropped onto the photocatalyst layer of the photocatalyst for evaluation was then measured. The fading rate of methylene blue was measured using a black-and-white reflection densitometer (Ihara Electronics Co., Ltd., "R700") to measure the reflection density of methylene blue on the photocatalyst layer and determine the difference δ in reflectance (unit: %). The fading of methylene blue is caused by the photodecomposition of methylene blue dropped onto the photocatalyst layer of the photocatalyst for evaluation. The smaller the difference δd in reflectance, which indicates the fading rate of methylene blue, the better the methylene blue decomposition activity of the photocatalyst layer formed by the photocatalytic coating.

[0075] The measurement results of the methylene blue fading rate of the evaluation photocatalysts 1 to 20 are shown in Table 2. The evaluation criteria for the methylene blue decomposition test are as follows. ◯: The reflectance difference Δd is less than 20%. Δ: The reflectance difference Δd is 20% or more and less than 50%. ×: The difference Δd in reflectance is 50% or more and 100% or less.

[0076] The evaluation of the methylene blue decomposition test for the evaluation photocatalysts 1 to 18 formed using the photocatalyst coatings 1 to 15 (Examples 1 to 15) and the photocatalyst coatings 16 to 18 (Comparative Examples 16 to 18) was "Good." It is believed that the photocatalytic activity was not inhibited by the binder because the ratio of the binder mass to the total mass of the binder and photocatalyst in these photocatalyst coatings was less than (20 / 100). The evaluation of the methylene blue decomposition test for the evaluation photocatalysts 19 and 20 formed using the photocatalytic paints 19 and 20 (Comparative Examples 19 and 20) was "X." Since the ratio of the mass of the binder to the total mass of the binder and photocatalyst in these photocatalytic paints was (30 / 100), it is thought that the photocatalytic activity was inhibited by the binder.

[0077] The results of the overall evaluation of the evaluation photocatalysts 1 to 20 in the durability test and methylene blue decomposition test are shown in Table 2. The evaluation criteria for the overall evaluation are as follows: ◯: No △ or × evaluations were given in the durability test and methylene blue decomposition test. △: In the durability test and the methylene blue decomposition test, there was a △ rating and no × rating. ×: At least one poor (NG) evaluation was found in the durability test and the methylene blue decomposition test. [Explanation of symbols]

[0078] 2: Photocatalytic paint 3: Substrate 4: Coating layer 5: Photocatalytic layer 6: Container 10: Photocatalytic coating 12: Photocatalytic particles 13: Dehydration condensation product of first binder 14: Dehydration condensation product of second binder

Claims

1. The photocatalytic composition includes photocatalytic particles containing tungsten oxide, a binder, and an aqueous dispersion medium, the binder includes a first binder and a second binder, or includes a dehydration condensate of the first binder and the second binder; the first binder is a compound containing a trihydroxysilane group or a dehydration condensate of the compound, The second binder is a photocatalytic paint that is an aliphatic hydroxy acid or an aldonic acid.

2. The compound containing a trihydroxysilane group has the chemical formula (1): R 1 -Si(OH) 3 [In the formula, R 1 represents an organic group having an epoxy group, an organic group having an amino group, an organic group having a methacryl group, or an organic group having a mercapto group, 2. The photocatalytic coating material according to claim 1, wherein the second binder is a compound having one to five hydroxyl groups and one to three carboxyl groups.

3. R in chemical formula (1) 1 The photocatalytic coating material according to claim 2, wherein represents a 3-glycidoxypropyl group, a 3-aminopropyl group, a 3-methacryloxypropyl group, or a 3-mercaptopropyl group.

4. The photocatalytic paint according to claim 1, wherein the ratio (b / a) of the mass (b) of the binder to the total mass (a) of the photocatalytic particles and the binder in the photocatalytic paint is (1 / 100) or more and (25 / 100) or less.

5. The photocatalytic paint according to claim 1, wherein the ratio (c / a) of the mass (c) of the photocatalytic particles to the total mass (a) of the photocatalytic particles and the binder in the photocatalytic paint is (75 / 100) or more and (99 / 100) or less.

6. The photocatalytic paint according to claim 1, wherein the ratio (e / d) of the mass (e) of the second binder to the mass (d) of the first binder in the photocatalytic paint is (5 / 95) or more and (40 / 60) or less.

7. 2. The photocatalytic coating material according to claim 1, wherein the second binder is gluconic acid, citric acid, malic acid or lactic acid.

8. Further containing a preservative, The photocatalytic coating material according to claim 1 , wherein the preservative contains at least one of copper ions, silver ions, and zinc ions.

9. A photocatalytic coating method comprising the steps of: applying the photocatalytic coating material according to any one of claims 1 to 8 onto a substrate to form a coating layer; and air-drying the coating layer.

10. A substrate and a photocatalytic layer provided on the substrate, the photocatalyst layer includes photocatalyst particles containing tungsten oxide and a dehydration condensate of a first binder and a second binder, the first binder is a compound containing a trihydroxysilane group or a dehydration condensate of the compound, The photocatalytic coating wherein the second binder is an aliphatic hydroxy acid or an aldonic acid.

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